Small precision metering pumps, designed for metering, for example, viscous materials such as hot melt adhesive or molten nylon or other polymers, in certain applications include a housing enclosing a pair of circular gears with external, intermeshing teeth. The gears are disposed within a pump cavity between a pair of housing plates, with the side surfaces of the gears in direct, sealed engagement with the plates to prevent internal fluid leakage between the high and low pressure zones in the pump cavity. Fixed thrust or wear plates are sometimes provided between the gear plates and the housing plates to reduce or eliminate wear and provide the necessary fluid seal. Various vents and grooves have been provided in the plates to balance the plates against the gears.
Inlet and outlet passages in the housing direct the viscous material into and out of discharge grooves formed in the surface of one or both plates, adjacent the intermeshing teeth, so that the gears meter the viscous fluid upon rotation. One of the gears (the drive gear) rotates on a drive shaft permanently mounted within the housing and extending outwardly therefrom. The drive shaft is typically journaled on a bushing mounted within the housing for smooth rotation of the gears over a range of operating torques and pressures. Appropriate O-seals supported by the housing seal around the drive shaft to prevent fluid from leaking out of the pump, and contaminants from entering the pump. The drive shaft is remotely connected to the drive shaft of a motor (prime mover), typically by a female-to-female connector.
The other, secondary gear of the set can be mounted for example, on a fixed stud or arbor supported between the housing plates. For more viscous materials, the secondary gear may also be driven by a second drive shaft permanently mounted within the housing, journaled on a second bushing, and remotely connected to a second prime mover. The stud for the secondary gear is supported generally parallel to the drive shaft for the drive gear. Alternatively, or in addition, a second set of circular gears can be provided, with external teeth, mounted adjacent the first set of gears in the same manner as described above. Such a second set of gears also facilitates pumping highly viscous material through the pump.
U.S. Pat. Nos. 2,818,023; 3,499,390; 4,277,230 and 5,496,163, for example, illustrate metering pumps such as described above.
While the precision metering pumps described above have been found appropriate for many applications, it is believed that the pumps are still too large for some applications, and that the industry has been demanding still further reductions in size. The use of a pump drive shaft and associated bushings, while heretofore believed necessary, serve to increase the over-all size of the pump. In some applications, a substantial number of pumps are mounted together on large spinning or processing machines, and the size of each pump can be an impediment to reducing the over-all size (and cost) of the machines.
As such, it is believed that there is a demand in the industry for an improved precision metering pump which has a reduced size, and which still operates effectively over a broad range of operating conditions. It is also believed there is a continual demand in the industry for metering pumps of a compact size which are easy to manufacture and assemble, and which are reliable over a long operating lifetime.